Time and Work - General Aptitude

Q1:

A can do a work in 15 days and B in 20 days. If they work on it together for 4 days, then the fraction of the work that is left is :

A
1
4

B
1
10

C
7
15

D
8
15

ANS:D -

8
15

A's 1 day's work = 1 ;
15
B's 1 day's work = 1 ;
20
(A + B)'s 1 day's work = ( 1 + 1 ) = 7 .
15 20 60
(A + B)'s 4 day's work = ( 7 x 4 ) = 7 .
60 15
Therefore, Remaining work = ( 1 - 7 ) = 8 .
15 15